Semiconductor devices that use silicon carbide (SiC) semiconductor substrates in order to allow the semiconductor devices to be made, for example, higher in breakdown voltage, lower in loss and usable in a high temperature environment, and that are superior in withstand voltage and heat resistance to silicon (Si) semiconductor devices, are applied to power semiconductor devices such as a MOSFET (metal-oxide-semiconductor field-effect transistor), a schottky barrier diode and the like. For example, in the case of a SiC semiconductor MOSFET with a breakdown voltage class of 1 to 1.2 kV, there is provided an ON-resistance of 5 mΩ cm2 or less, the resistance value of which is half or less when compared with a Si semiconductor MOSFET or IGBT (Insulated Gate Bipolar Transistor) with the same breakdown voltage. The reason why the use of a SiC semiconductor can largely reduce the ON resistance in comparison with a Si semiconductor, is that the SiC semiconductor has a high dielectric-breakdown electric field and allows a voltage-withstanding layer (drift layer) for achieving the same breakdown voltage to be thinner than that of the Si semiconductor, and further allows the doping amount of impurities for the voltage withstand layer to be higher, and something like that. It is thought that, hereafter, replacement of most of Si semiconductor IGBTs by these devices as inverter components will be facilitated with achievement of: improvement in terms of their manufacturing cost; enhancement in their process technology; and other enhancement in their capabilities.
Heretofore, as a method of establishing bonding between a semiconductor substrate and an electrode at the time of manufacturing a front-to-back conductive semiconductor device, such a method is proposed that comprises a step of forming a semiconductor element structure on the major surface side of a silicon semiconductor substrate and thereafter, in the last process, grinding the back-surface side of the silicon semiconductor substrate and ion-implanting therein impurities whose conductivity type is the same as that of the back surface, and then forming thereon a metal thin film to be provided as an electrode (see, for example, Patent Document 1).
Meanwhile, as a method of establishing assured bonding while reducing power loss at the time of forming an electrode onto a silicon nitride (SiC) semiconductor substrate, such a method is proposed in which, with respect to a semiconductor element provided with the SiC substrate, a heat treatment is locally applied by optical heating to the electrode on the back surface of the substrate and at that treatment, its procedure and the conditions for the heat treatment are optimized, so that the semiconductor element can be manufactured in a good yield (see, for example, Patent Document 2).